Chemistry - A Molecular Science

Glossary

The

percent yield

is the fraction of the theoretical

yield, expressed as a percent, that is actually isolated in a chemical reaction.

A

period

in the periodic table is

a horizontal row. The

properties of the elements in a period vary gradually across the period.

The

periodic law

states that the elements exhibit a

periodicity in the chemical

and physical properties

when they are arranged in the order of their atomic numbers.

The

periodic table or chart

is an arrangement of the

elements into rows (periods) and columns (groups) such that the elements in the same group have similar properties.

pH

is the negative base 10 logarithm of the hydronium ion concentration in a solution.

pH = -log[H

O 3

1+]

A

phase diagram

shows the state of a substance as a

function of its temperature and pressure.

A

photon

is a quantum of energy in the form of

electromagnetic radiation.

Photosynthesis

is the process in which plants use solar

energy to covert CO

and H 2

O into carbohydrates. 2

A

physical property

is one that is independent of other

substances. Melting point, boiling point, color, and hardness are some physical properties.

A

pi (

) bondπ

is formed from the side-on interaction of

two p orbitals. Pi bonds have nodal planes that contain the internuclear axis.

The

pK

of an acid is the negative base 10 logarithm of a

the acid dissociation constant. pK

= -log Ka

(^) a
Planck’s constant (h)
is the proportionality constant
that relates the frequency of a photon to its energy. h = 6.626 x 10
-34
J/s
A
polar covalent bond
is a covalent bond in which the
bonding electrons are NOT shared equally. Thus, the bonds are between atoms of different electronegativities.
Polar molecules
have asymmetric charge distributions.
The result is a molecular dipole.
The
polarizability
of an atom or molecule is a measure
of the ease with which its electron cloud can be deformed.
A
polyamide
is a condensation polymer that contains
many amide linkages. Nylons and peptides are polyamides.
A
polyatomic ion
is an ion, such as CO
2-, in which 3
two or more atoms are covalently bound.
A
polyene
is an organic compound with many double
bonds.
A
polymer
is a large molecule consisting of many
single unit building blocks called mers.
A
polypeptide
is a polyamide produced from the
reaction of many amino acids.
Polyprotic acid acids
have more than one acidic
proton. Examples: H
SO 2
is a diprotic acid and 4
H^3
PO
is a triprotic acid. 4
Polyunsaturated
organic compounds contain many C-
C multiple bonds.
A
positron
is an elementary particle with the mass of
an electron and a positive charge. It is the antimatter analog of the electron.
Positron decay
is the emission of a positron from the
nucleus. Positron decay increases the neutron/proton ratio, so it is common in nuclei that lie below the band of stability.
Potential energy
is energy due to position. In
chemistry, potential en
ergy arises from the
interaction of charged partic
les, and the closer they
are, the stronger they interact.
A
precipitate
is a solid formed when two solutions are
mixed, or the act of forming the solid. Thus, AgCl precipitates and is a precipitate when it does.
The
precision
of a number is given by the number of
significant figures to which it is reported. 1.00 m is more precise than 1.0 m.
A
pre-exponential
precedes an exponential. Typically
used in the Arrhenius equation: k = Aexp{-
E/RT
},
where A is the pre-exponential.
Pressure (P)
is force per unit area: P = F/A.
Pressure-volume or PV work
is done when the
volume of a gas changes against an external pressure.
The
principal quantum number (n)
specifies the
energy level of an el
ectron in an atom.
A
protein
is a large polypeptide.
A
proton
is a subatomic particle found in the nucleus.
It carries a +1 charge and has a mass of ~1 amu.
A
proton acceptor
is called a Brønsted base.
A
proton donor
is called a Brønsted acid.
A
purely covalent bond
is a covalent bond in which
the bonding electrons are shared equally. Thus, the bonds between atoms of the same electronegativity are purely covalent.

Q

A

qualitative observation

is one that does not involve

numbers.

A

quantitative observation

is one that does involve

numbers.

A

quantity

in the factor label method is an amount and

is characterized by a sing

le unit. For example, 3 m

is a quantity, but 3 m/s is a factor.

A

quantum

is a packet of energy.

© by

North

Carolina

State

University